JP5680978B2 - COMMUNICATION DEVICE, COMMUNICATION METHOD, AND COMMUNICATION PROGRAM - Google Patents

Description

  The present invention relates to a communication device and a communication method performed by the communication device.

  With the spread and development of communication technology, data transmission / reception is increasing through a wide area network (WAN) including the Internet. For example, a system is increasing in which user terminals transmit data to opposing devices via WAN, and the opposing devices perform processing based on received data. In such a system, since processing is not performed unless the data transmitted from the user device is received by the opposite device, if the data transmission fails, the user device retransmits the transmission data to the opposite device again. . For example, when the user terminal cannot receive an acknowledgment message for a transmitted packet before the retransmission timeout (Retransmission Time Out, RTO) elapses, the user terminal transmits the transmitted packet to the opposite device again.

  As a related technique, there has been proposed a communication device that uses a measurement result of a round-trip time in which data reciprocates between the server device and the communication device when calculating a retransmission timeout until the communication data to be transmitted to the server device is retransmitted. Yes. This communication apparatus does not use the round trip time measurement result, which is larger than the retransmission timeout calculation result, for the next retransmission timeout calculation.

JP 2008-172480 A

  Depending on the user terminal, the retransmission timeout may be set to a fixed value. However, the round-trip time of the packet between the user device and the opposite device varies depending on the congestion state of the network. For example, when the number of packets transmitted and received through the network is small, the round trip time is shortened. Therefore, when the retransmission timeout is set to a fixed value, the time from when a packet is transmitted until the packet is retransmitted may be too long. In the background art, the case where the data transmitted from the user apparatus is processed by the opposite apparatus has been described, but the same problem occurs when any of a plurality of communication apparatuses transmit and receive packets via the WAN. there is a possibility.

  An object of the present invention is to change the time until retransmission is performed according to the round trip time of a packet for a packet transmitted from a device whose retransmission timeout is set to a fixed value.

  The communication apparatus according to the embodiment includes a reception unit, a storage unit, a transmission unit, a measurement unit, and a retransmission unit. The receiving unit transmits the first and second packets addressed to the opposite device, and sends the first and second packets from the transmission source device that retransmits the packet that cannot be confirmed by the opposite device to the opposite device. Receive. The storage unit stores the first and second packets. The transmission unit transmits the first and second packets to the opposite device. The measurement unit receives the first response message for notifying the reception of the first packet at the opposite device from the time when the transmission unit transmits the first packet to the opposite device. Measure response time, which is the time to time. Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite device, the reception unit notifies the reception of the second packet by the opposite device. If no response message 2 is received and no retransmission packet is received from the transmission source device, the retransmission unit operates. Here, the retransmission packet is a packet obtained by retransmitting the second packet from the transmission source device. The retransmission unit acquires the second packet from the storage unit and causes the transmission unit to transmit the second packet to the opposite device again.

  Also for a packet transmitted from a device whose retransmission timeout is set to a fixed value, the time until retransmission is changed according to the round trip time of the packet.

It is a figure explaining the example of operation | movement of the communication apparatus concerning a certain embodiment. It is a figure which shows the example of a structure of a communication apparatus. It is a figure which shows the example of a directly connected apparatus table. It is a figure explaining the example of the detection method of a directly connected apparatus. It is a figure which shows the structural example of an IP header and a TCP header. It is a figure which shows the example of the recording method of the detected connection. It is a figure which shows the example of a communication packet table. It is a figure which shows the example of a connection table and a communication packet table. It is a figure which shows the example of a communication packet table. It is a figure which shows the example of a connection table and a communication packet table. It is a flowchart explaining the example of the operation | movement performed when a communication apparatus receives a packet. It is a flowchart explaining the example of the operation | movement performed when a communication apparatus receives a packet. It is a flowchart explaining the example of operation | movement when the packet stored in the communication apparatus is resent to an opposing apparatus. It is a table which shows the example of the time after the packet transmitted to the opposite apparatus is transmitted until it is resent. It is a flowchart explaining the example of the operation | movement performed when a communication apparatus receives a packet. It is a flowchart explaining the example of the operation | movement performed when a communication apparatus receives a packet.

  FIG. 1 is a diagram illustrating an example of the operation of the communication device 10 according to an embodiment. The communication device 10 relays the packet transmitted from the transmission source device 2 toward the opposite device 6. When a packet transmitted from the transmission source device 2 to the opposite device 6 is not notified at a certain time that the packet has been received by the opposite device 6, and when the packet is not retransmitted from the transmission source device 2, communication is performed. The device 10 retransmits the packet to the opposite device 6. The operation of the communication apparatus 10 when a packet is transmitted from the transmission source apparatus 2 to the opposite apparatus 6 via the WAN 4 will be described with reference to FIG.

  In the following description, the time from the time when a certain packet is transmitted from the communication device 10 to the opposite device 6 until the time when the response message notifying the reception of the packet is received by the communication device 10 is referred to as “response time”. (Round Trip Time, RTT). Furthermore, after the packet transmitted from the transmission source device 2 is transmitted to the opposite device 6, the time that the communication device 10 waits until the same packet is retransmitted to the opposite device 6 may be described as “waiting time”.

  (1) First, the transmission source device 2 transmits a first packet toward the opposite device 6. When the communication device 10 receives the first packet, the communication device 10 duplicates the received packet and associates the duplicated first packet with a combination of information identifying the transmission source device 2 and information identifying the communication device 10. Remember.

(2) The communication device 10 transmits the first packet to the opposite device 6 that is the destination of the packet. Further, the communication device 10 stores the time when the first packet is transmitted.
(3) Upon receiving the first packet, the opposite apparatus 6 transmits a first response message notifying that the first packet has been received, to the transmission source apparatus 2. When the first response message reaches the communication device 10, the communication device 10 refers to the first response message and recognizes that the first packet has been received by the opposite device 6. Next, the communication device 10 obtains a time (response time) between the time when the first packet is transmitted from the communication device 10 and the reception time of the first response message. 1A shows the response time.

(4) The communication device 10 transmits the first response message to the transmission source device 2.
(5) Next, for the second packet transmitted from the transmission source device 2, the communication device 10 duplicates and stores the second packet in the same manner as in the procedure (1). Further, the time when the second packet is transmitted to the opposite apparatus 6 is also stored.

  (6) Furthermore, the communication device 10 transfers the second packet to the opposite device 6. Here, it is assumed that packet loss occurs in WAN 4 for the second packet. In this case, since the opposite apparatus 6 does not receive the second packet, the opposite apparatus 6 does not transmit the second response message notifying the reception of the second packet.

  (7) The communication device 10 calculates the standby time using the response time obtained in the procedure (3). Here, as shown in FIG. 1B, the standby time is longer than the response time. A method for calculating the standby time will be described later. The communication device 10 waits until the standby time elapses from the time when the second packet is transmitted to the opposite device 6. If the communication device 10 does not receive the second response message and the second packet retransmitted from the transmission source device 2 toward the opposite device 6 is not received even after the standby time has elapsed, the communication device 10 Transmits the stored second packet to the opposite apparatus 6.

  (8) When the opposite device 6 receives the second packet retransmitted in the procedure (7), the opposite device 6 transmits a second response message to the transmission source device 2. The communication device 10 recognizes that the second packet has been received by the opposite device 6 by confirming the second response message.

(9) The communication device 10 transmits the second response message to the transmission source device 2.
As described above, when the reception of the packet at the opposite device 6 cannot be confirmed before the standby time elapses from the transmission time of the packet, and the packet is not retransmitted from the transmission source device 2, the communication is performed. The device 10 retransmits the packet to the opposite device 6. Here, since the waiting time is calculated based on the response time, the length of the waiting time varies according to the variation of the response time. Therefore, the communication device 10 can change the retransmission timing of the packet transmitted from the transmission source device 2 according to the response time. For example, in the transmission source device 2, even when the retransmission timeout is set to a fixed value, the communication device 10 can retransmit the packet at a timing calculated according to the response time. That is, when the response time is short, the communication device 10 operates to shorten the interval from the packet transmission time to the packet retransmission time. For this reason, for example, when an application operating on the opposite device 6 processes data transmitted from the transmission source device 2, even if packet transmission fails, the packet is sent in time for processing in the application. Probability of resending increases.

<Device configuration>
FIG. 2 is a diagram illustrating an example of the configuration of the communication device 10. The communication device 10 includes a reception unit 11, a transmission unit 12, a routing unit 13, a timer 14, a storage unit 20, and a retransmission substitution unit 30. The storage unit 20 includes a directly connected device table 21, a connection table 22, a communication packet table 23, and a routing table 24. The retransmission substitution unit 30 includes a directly connected device detection unit 31, a connection detection unit 32, a communication packet confirmation unit 33, a measurement unit 34, a calculation unit 35, a determination unit 36, and a retransmission unit 37.

  The receiving unit 11 receives a packet from the transmission source device 2. Further, the reception unit 11 can output the received packet to the directly connected device detection unit 31, the transmission unit 12, and the like. In addition, the receiving unit 11 receives a response message for notifying reception of a packet from the opposite device 6. The reception unit 11 outputs the received response message to the directly connected device detection unit 31, the transmission unit 12, and the like. The transmission unit 12 transmits the packet received from the transmission source device 2 toward the opposite device 6. The transmission unit 12 refers to the communication packet table 23 and retransmits the packet to the opposite device 6 when the standby time has elapsed from the time when the packet was transmitted to the opposite device 6. As will be described later, in the communication packet table 23, a packet transmitted from the transmission source device 2 to the opposite device 6 but not confirmed to be received by the opposite device 6 and information about the packet are recorded. Yes. Further, the transmission unit 12 transmits the response message received from the opposite device 6 to the transmission source device 2. The routing unit 13 determines the transfer destination of the packet received by the communication device 10 based on the routing table 24 and notifies the transmission unit 12 of the transfer destination. The timer 14 provides time information to the directly connected device detection unit 31, the connection detection unit 32, the communication packet confirmation unit 33, the measurement unit 34, the retransmission unit 37, and the like.

  The directly connected device detection unit 31 detects devices belonging to the same network as the communication device 10 and records information on the detected devices in the directly connected device table 21. In the following description, a communication device belonging to the same network as the communication device 10 may be referred to as “directly connected device”. The directly connected device may be the transmission source device 2. For example, it is assumed that the communication device A is a directly connected device and that the communication device A transmits a packet toward the communication device B. When a packet transmitted from the communication apparatus A to the communication apparatus B is transmitted to the communication apparatus B via the communication apparatus 10, the communication apparatus A becomes the transmission source apparatus 2 illustrated in FIG. An example of the directly connected device table 21 is shown in FIG. In the example of FIG. 3, the directly connected device table 21 stores a Media Access Control (MAC) address, an Internet Protocol (IP) address, and the latest communication time with the communication device 10 of the directly connected device. Note that FIG. 3 is an example of the directly connected device table 21, and the information included in the directly connected device table 21 may be appropriately changed according to the implementation.

  When communication using Transmission Control Protocol (TCP) is performed between the transmission source device 2 and the opposite device 6, the connection detection unit 32 refers to the TCP header in the transmitted / received packet. The connection detection unit 32 monitors the generation and disappearance of the connection based on the information included in the TCP header, and stores information related to the connection in which communication is performed in the connection table 22. A connection monitoring method and an example of the connection table 22 will be described later.

  The communication packet confirmation unit 33 updates the connection table 22 and the communication packet table 23 based on the packet received from the transmission source device 2. Information such as packet transmission time is recorded in the communication packet table 23.

  The measurement unit 34 obtains a response time from the difference between the time when the response message for the packet recorded in the communication packet table 23 is received by the reception unit 11 and the transmission time of the packet. Further, the measurement unit 34 deletes information related to the packet that has received the response message from the opposite device 6 among the information recorded in the communication packet table 23. For this reason, the communication packet table 23 stores information on packets for which the response message from the opposite device 6 is not received by the communication device 10 among the packets transmitted from the communication device 10 to the opposite device 6.

  Based on the response time, the calculation unit 35 determines the waiting time from the time when a packet is transmitted from the transmission unit 12 to the opposite device 6 until the time when the retransmission unit 37 instructs the transmission unit 12 to retransmit the packet. calculate. A method for calculating the standby time will be described later.

  The determination unit 36 determines whether the communication device 10 performs retransmission for the opposite device 6 instead of the transmission source device 2. For example, the determination unit 36 determines whether the time from when the transmission source device 2 transmits a packet until the same packet is retransmitted is longer than the standby time. For the transmission source device 2 that is determined to take longer than the standby time for packet transmission, the communication device 10 retransmits the packet. Further, in the following description, when the communication device 10 performs retransmission to the opposite device 6 instead of the transmission source device 2, the transmission source device 2 may be described as a “target device”.

  The retransmission unit 37 refers to the communication packet table 23, and among the packets transmitted from the target device, packets for which no response message has been received from the opposite device 6 until the standby time elapses from the packet transmission time. Identify. The retransmission unit 37 instructs the transmission unit 12 to retransmit the packet based on the data included in the communication packet table 23.

  Next, an example of the hardware configuration of the communication device 10 will be described. The communication device 10 can include, for example, a processor such as a Central Processing Unit (CPU), a memory, and a network connection device. In this case, the network connection device connects the communication device 10 to the network and operates as, for example, the reception unit 11 and the transmission unit 12. The CPU can operate as the retransmission alternative unit 30, the routing unit 13, the timer 14, and the like. The memory operates as the storage unit 20. For example, the communication device 10 may be a computer including a processor, a memory, and a network connection device. The configuration described here is an example, and the configuration of the communication device 10 may be changed depending on the implementation.

<First Embodiment>
The communication device 10 performs detection of a directly connected device, measurement of a response time, detection of a connection, retention of a packet received from the directly connected device, calculation of a waiting time, retransmission of a packet, and the like. Details of these operations will be described below.

[Detection of directly connected devices]
When the communication device 10 is activated, the communication device 10 first detects a device (directly connected device) that may be the transmission source device 2. The directly connected device detection unit 31 uses an Address Resolution Protocol (ARP) request packet for detecting directly connected devices.

  FIG. 4 is a diagram illustrating an example of a method for detecting a directly connected device. When a device that is to start communication acquires an IP address of a communication destination, the device transmits an ARP request packet to acquire the MAC address of the device that uses the IP address. FIG. 4 shows an example of the ARP request packet transmitted from the device A. In the following example, it is assumed that the IP address of device A is “IP1” and the MAC address is “MAC1”. The ARP request packet includes an Ethernet header and an ARP message. In the Ethernet header, a transmission destination MAC address, a transmission source MAC address, and Type are recorded. Here, the source MAC address is recorded as the MAC address of the device A, and the Type is recorded as “0806” indicating an ARP request. Further, “ff: ff: ff: ff: ff: ff”, which is a broadcast address (MAC_B), is used as the transmission destination MAC address of the ARP request packet. For this reason, the ARP request packet is transmitted to all communication devices belonging to the same network as the network to which the device A belongs.

  The ARP message of the ARP request packet includes Opcode, source MAC address, source IP address, target MAC address, and target IP address. Here, the target IP address is an IP address used in a device that attempts to acquire a MAC address. For example, the target IP address is an IP address of a target device with which the device A communicates. The target MAC address is the MAC address to be acquired. When the ARP request packet is generated, since device A has not acquired the target MAC address, “0” is recorded instead of the MAC address. Opcode is information indicating whether the ARP message is an ARP request, and is “1” in the case of an ARP request. The MAC address and IP address of device A are stored in the source MAC address and source IP address fields.

  When the device A broadcasts the ARP request packet shown in FIG. 4, the communication device 10 belonging to the same network as the device A receives the ARP request packet. The directly connected device detection unit 31 confirms the type of the packet received via the reception unit 11 and acquires an ARP request packet. Further, the directly connected device detection unit 31 extracts the source MAC address and the source IP address from the acquired ARP message of the packet, and stores them in the directly connected device table 21 (FIG. 3). In addition, the directly connected device detection unit 31 refers to the timer 14, acquires the time when the ARP request packet is received, and stores it in the directly connected device table 21. Each time the communication device 10 receives an ARP request packet, the directly connected device detection unit 31 acquires the transmission source IP address, the transmission source MAC address, and the reception time of the ARP request packet included in the ARP request. Store in table 21.

  When the ARP request packet is received again from the device already registered in the directly connected device table 21, the directly connected device detecting unit 31 changes the last communication time of the record relating to the device that has transmitted the ARP request packet. For example, communication with the device A has already been recorded in the top column of the directly connected device table 21 in FIG. Therefore, when the directly connected device detection unit 31 receives the ARP request packet from the device A, it changes the last communication time with the device A to the reception time of the ARP request packet. In addition, each time the directly connected device detection unit 31 receives a connection generation request or a packet transmitted via an already established connection, the directly connected device detection unit 31 sets the final communication time associated with the source address of those packets. Update.

[Detection of connection]
Next, an example of an operation performed in the communication device 10 when the device recorded in the directly connected device table 21 generates a connection with the opposite device 6 will be described. In the following description, it is assumed that the IP address of the transmission source device 2 is IP1 and the IP address of the opposite device 6 is IP10. In the following description, it is assumed that the transmission source device 2 and the opposite device 6 communicate via the WAN 4 as shown in FIG.

  When receiving the packet, the receiving unit 11 outputs the received packet to the directly connected device detecting unit 31. The directly connected device detection unit 31 determines whether the packet is a packet transmitted from the directly connected device by checking the IP header for packets other than the ARP request packet.

  FIG. 5A shows a configuration example of the IP header. FIG. 5A shows an IP header used in IPv4. The IPv4 header includes a packet source IP address and a destination IP address. Further, the IPv4 header includes a header length field and a data length field. The header length field indicates the length of the IP header. The data length field indicates the combined length of the IP header and segment data. Further, the IPv4 header includes fields such as version information, service type, identification number, flag, fragment offset, Time To Live (TTL), protocol, header checksum, option, and padding. Although the IPv4 header has been described here, the IPv6 header also includes a source IP address and a destination IP address. The IPv6 header includes a payload length field. In the payload length field, the length of the payload obtained by subtracting the length of the IPv6 header from the entire length of the IPv6 packet is recorded.

  The directly connected device detection unit 31 compares the source IP address included in the IP header of the received packet with the IP address included in the directly connected device table 21. When the transmission source IP address of the received packet is recorded in the direct connection device table 21, the direct connection device detection unit 31 determines that the transmission source device of the packet is a direct connection device, and sends it to the connection detection unit 32. Output the packet. The connection detection unit 32 acquires information related to the connection by referring to the TCP header of the packet input from the directly connected device detection unit 31. The connection detection unit 32 stores the acquired information in the connection table 22.

  FIG. 5B is a diagram illustrating a configuration example of the TCP header. The TCP header includes a source port number, a destination port number, a sequence number, an acknowledgment number, and a control bit. Furthermore, the TCP header includes options, data offset, reserved bits, window size, checksum, urgent pointer, and padding. In the data offset field, the length of the TCP header is recorded. The control bits include 6 bits of URG (urgent), ACK (acknowledge), PSH (push), RST (reset), SYN (synchronize), and FIN (finis). In the communication device 10, control using values of ACK, RST, SYN, and FIN is performed. The SYN bit indicates whether connection establishment is requested. The packet with SYN = 1 is used for requesting the destination device to establish a connection. In the following description, a packet with SYN = 1 may be described as a “transmission permission request packet”. The ACK bit indicates whether the packet is a response message. A packet with ACK = 1 is used as a response message for a certain packet. RST and FIN indicate whether the connection used for transmitting the packet is requested to be disconnected. A packet in which either RST or FIN is 1 requests the destination device of the packet to disconnect the connection used to transmit the packet.

  The connection detection unit 32 confirms the values of RST, SYN, and FIN among the control bits in the TCP header for each packet input from the directly connected device detection unit 31. Here, it is assumed that the communication apparatus 10 has received a packet with SYN = 1, RST = 0, and FIN = 0. When SYN is 1, the connection detection unit 32 determines that a connection from the transmission source device 2 to the opposite device 6 is established, and records information on the established connection in the connection table 22.

  FIG. 6 is a diagram illustrating an example of a method for recording the detected connection. The connection table 22 records, for example, the IP address of the transmission source device 2, the transmission source port number, the IP address of the opposite device 6, the destination port number, and the sequence number (NextSeqNo) of the segment to be transmitted next. Furthermore, the retransmission timeout (RTO calculation value) calculated from the response time, the retransmission flag, and the last communication time are stored. In the following description, the retransmission timeout in the communication apparatus 10 calculated from the response time may be described as “RTO calculation value”. Here, the retransmission flag is used for the communication apparatus 10 to identify the transmission source apparatus 2 that performs retransmission of the packet. When the retransmission flag is “ON”, the communication device 10 retransmits the packet transmitted through the connection without performing the determination by the determination unit 36. Note that the calculation unit 35 can change the calculation method of the standby time depending on whether the retransmission flag is “ON” or “OFF”. Hereinafter, the operation of the connection detection unit 32 will be described with reference to FIG.

  When the connection detection unit 32 receives the transmission permission request packet, the connection detection unit 32 acquires the transmission source IP address and the destination IP address from the IP header of the packet and records them in the connection table 22. The connection detection unit 32 records the transmission header port number of the TCP header in the connection table 22 as the port number of the transmission source device 2 and the destination port number of the TCP header as the port number of the opposite device 6. The connection detection unit 32 also records the time when the packet is received in the connection table 22.

Next, the connection detection unit 32 calculates the sequence number of the segment to be transmitted next. The connection detection unit 32 obtains the length of the segment data by subtracting the value recorded in the header length field from the value recorded in the data length field of the IPv4 packet. Next, the connection detection unit 32 obtains the value of the data included in the packet by acquiring the value of the data offset field of the TCP header and subtracting the length of the TCP header from the length of the segment data. That is, assuming that the data length included in the packet is D, the value of the data length field of the IPv4 packet is IPd, the IP header length is IPh, and the TCP header length is TCPh, the connection detection unit 32 calculates the data length by the following calculation. D is obtained.
D = IPd-IPh-TCPh

Further, the connection detection unit 32 calculates the sequence number (NextSeq) of the segment to be transmitted next by adding the data length to the sequence number (Seq) included in the packet received by the communication device 10. That is, the sequence number of the segment to be transmitted next is obtained by the following equation. The connection detection unit 32 records the calculated NextSeq in the connection table 22.
NextSeq = Seq + D

  As shown in FIG. 6, the connection detection unit 32 records NextSeq in the connection table 22. If the value of NextSeq is calculated based on a packet that does not contain data, such as a transmission permission request packet, the sequence number of the data contained in the next packet transmitted through the same connection is May be greater than NextSeq. For example, since a transmission permission request packet transmitted from the transmission source device 2 to the opposite device 6 to establish a connection does not include transmission data from the transmission source device 2 to the opposite device 6, the data length is 0. Become a byte. When the sequence number of the packet transmitted for establishing the connection is 2000, the connection detection unit 32 sets NextSeq to 2000. However, the sequence number included in the packet transmitted next to the transmission permission request packet may be larger than 2000.

  Further, the connection detection unit 32 acquires time information from the timer 14 and records it in the connection table 22. When a request for establishing a connection is transmitted from the transmission source device 2 to the opposite device 6, since the response time between the transmission source device 2 and the opposite device 6 has not yet been obtained, the RTO calculation value is not recorded. The connection detection unit 32 sets the retransmission flag to “OFF” for the detected connection.

  Next, the transmission permission request packet is stored in the communication packet table 23. FIG. 7 shows an example of the communication packet table 23. The communication packet table 23 stores, for example, the IP address of the transmission source device 2, the transmission source port number, the IP address of the opposite device 6, the destination port number, the sequence number of the packet, the data length, the number of retransmissions, and the transmission time. Further, the received packet is stored in the communication packet table 23 in association with these pieces of information.

  The connection detection unit 32 has already recognized the IP address of the transmission source device 2, the transmission source port number, the IP address of the opposite device 6, the destination port number, the sequence number of the packet, and the data length of the transmission permission request packet. ing. Therefore, the connection detection unit 32 stores these pieces of information in the communication packet table 23 and outputs a transmission permission request packet to the communication packet confirmation unit 33. The communication packet confirmation unit 33 sets the number of retransmissions to “0” when registering the packet in the communication packet table 23. Further, the communication packet confirmation unit 33 acquires time information from the timer 14 and records the time when the packet is output from the transmission unit 12 toward the opposite device 6 in the communication packet table 23.

[Measure response time and RTO calculation value]
Next, a case where a response message permitting transmission of a connection is transmitted from the opposite apparatus 6 to the transmission source apparatus 2 and the communication apparatus 10 receives the response message will be described.

  The reception unit 11 outputs the packet received from the opposite device 6 to the directly connected device detection unit 31. The directly connected device detection unit 31 compares the IP address included in the IP header of the packet with the IP address recorded in the directly connected device table 21. When the destination IP address is recorded in the direct connection device table 21, the direct connection device detection unit 31 outputs the packet to the measurement unit 34. Accordingly, a response packet to the transmission permission request packet transmitted to the opposite device 6 via the communication device 10 is output to the measurement unit 34.

  The measurement unit 34 refers to the ACK bit in the TCP header of the packet input from the directly connected device detection unit 31 and confirms whether a response message is received. When the value of the ACK bit is “1”, the measurement unit 34 determines that the response message has been received, and refers to the confirmation response number. In the confirmation response number, a sequence number for identifying the next data received by the opposite device 6 from the transmission source device 2 is recorded. For this reason, the measurement unit 34 recognizes that the packet including data having a smaller sequence number than the acknowledgment number has been received by the opposite device 6. However, at the stage where the connection is established, the packet registered in the communication packet table 23 in relation to the connection is only the transmission permission request packet transmitted from the transmission source device 2 to the opposite device 6. Therefore, the measurement unit 34 determines that the response message notifies the reception of the transmission permission request packet, and acquires the reception time of the response message. Next, the measurement unit 34 refers to the communication packet table 23 and sets a value obtained by subtracting the time from the reception time of the response message to the transmission time of the transmission permission request packet as the response time.

For example, as shown in FIG. 7, the time when the transmission permission request packet is transmitted from the communication apparatus 10 to the opposite apparatus 6 is 12:00:00, and the reception time of the response message is 12: 00.04. Let it be seconds. Then, the measurement unit 34
(12: 00: 0.04 seconds) − (12: 0: 0) = 0.04 seconds is the response time. The measurement unit 34 outputs the obtained response time to the calculation unit 35. Further, the measurement unit 34 deletes the record about the transmission permission request packet from the communication packet table 23.

The calculation unit 35 calculates the RTO calculation value and the standby time using the response time. The calculation unit 35 performs a calculation based on the equation (1) using the response time obtained for the first time for the connection, and obtains an RTO calculation value (RTO _cal ).
RTO _cal = SRTT + max (G, K × RTTVAR) (1)
here,
K = 4
SRTT = MRTT
RTTVAR = MRTT / 2
Suppose that MRTT (Measured RTT) is a response time obtained by the measurement unit 34. RTTVAR is one half of the response time. G is the granularity (resolution) of the clock used by the communication device 10 for measuring the response time.

For example, assuming that the response time is 0.04 seconds and the clock resolution is 0.05 seconds, the RTO calculation value is obtained as follows.
RTTVAR = MRTT / 2 = 0.04 / 2 = 0.02 (seconds)
SRTT = MRTT = 0.04 (seconds)
RTO _cal = 0.04 + max (0.05, 4 × 0.02) = 0.12 (seconds)
The calculation unit 35 records the obtained RTO calculation value in the connection table 22.

[Retention of packets received through recorded connections]
Next, an example of the operation of the communication packet confirmation unit 33 and the like when the communication device 10 receives a packet transmitted from the transmission source device 2 to the opposite device 6 via the connection recorded in the connection table 22. explain. If the received packet is not an ARP request packet, the connection detection unit 32 refers to the TCP header of the received packet and determines whether the packet is transmitted via a connection registered in the connection table 22. To do. When receiving a packet transmitted from the transmission source device 2 via a connection registered in the connection table 22, the connection detection unit 32 outputs the packet to the communication packet confirmation unit 33. For example, when a packet transmitted from the transmission source device 2 to the opposite device 6 is received, is the connection detection unit 32 transmitted via the connection registered in the connection table 22 using the IP address and the port number? Confirm. If the packet is transmitted through the registered connection, the connection detection unit 32 outputs the packet to the communication packet confirmation unit 33.

  The communication packet confirmation unit 33 compares the value obtained by adding the data length to the sequence number of the input packet with the numerical value recorded in NextSeqNo of the connection table 22. Here, the method for obtaining the data length is the same as in the case of the transmission permission request packet. When the sum of the sequence number and the data length is larger than the numerical value recorded in NextSeqNo, the communication packet confirmation unit 33 determines that the input packet includes data transmitted from the transmission source device 2 to the opposite device 6 for the first time. To do. On the other hand, when the sum of the sequence number and the data length is equal to or smaller than the numerical value recorded in NextSeqNo, the communication packet confirmation unit 33 determines that the input packet is a retransmission packet.

  FIG. 8A shows an example of the communication packet table 23. FIG. 8A shows the communication packet table 23 when three packets P1 to P3 are transmitted from the transmission source device 2 to the opposite device 6. In the following description, it is assumed that when the communication packet table 23 is updated as shown in FIG. 8A, all of the packets P1 to P3 are determined to include data to be transmitted for the first time.

  The communication packet confirmation unit 33 records the sequence number and data length included in the TCP header of the packet input from the connection detection unit 32 in the communication packet table 23. The communication packet confirmation unit 33 acquires the IP address, the transmission source port number, and the destination port number of the transmission source device 2 and the opposite device 6 with reference to the TCP header or the like as in the connection detection unit 32, and the communication packet table 23 To record. The communication packet confirmation unit 33 sets the number of retransmissions to “0” when registering the packet in the communication packet table 23. Further, the communication packet confirmation unit 33 acquires time information from the timer 14 and records the time when the packet is output from the transmission unit 12 toward the opposite device 6 in the communication packet table 23.

  Based on the packet information input from the connection detection unit 32, the communication packet confirmation unit 33 obtains a sequence number indicating the next data after the data transmitted from the transmission source device 2 to the opposite device 6 so far. Record in table 22. Furthermore, the communication packet confirmation unit 33 also updates the last communication time in the connection table 22.

  FIG. 8B shows an example of the connection table 22 when the packets P1 to P3 are transmitted. The packets P1 to P3 are all transmitted from the transmission source device 2 to the opposite device 6 using the same connection. Therefore, in the connection, data corresponding to the sequence number 2001 to 1000 bytes, the sequence number 3001 to 1000 bytes, and the sequence number 3001 to 1000 bytes are transmitted to the opposite device 6. Therefore, when any of the packets P1 to P3 is received by the opposite device 6, data up to the sequence number 5000 is transmitted to the opposite device 6. Therefore, when the packets P1 to P3 are received by the opposite device 6, the next packet transmitted to the opposite device 6 includes data starting from the sequence number 5001. Therefore, 5001 is recorded in NextSeqNo.

  Each time the communication packet confirmation unit 33 receives a packet from the connection detection unit 32, the communication packet confirmation unit 33 compares the value obtained by adding the data length to the sequence number of the packet with the numerical value recorded in NextSeqNo of the connection table 22. When the total value of the sequence number and the data length is larger than the numerical value recorded in NextSeqNo of the connection table 22, the communication packet confirmation unit 33 changes NextSeqNo to the obtained total value.

[Calculation of waiting time]
The communication device 10 transmits the packet recorded in the communication packet table 23 to the opposite device 6. When a packet including data such as the packets P <b> 1 to P <b> 3 is transmitted, the calculation unit 35 calculates the standby time using the RTO calculation value recorded in the connection table 22. The number of retransmissions and M, when the waiting time from the transmission time of the packet to the M-th retransmission and R _M, calculating unit 35 calculates according to the waiting time (2).
R _M = RTO _cal × 2 ^M-1 × V (2)
In the formula (2), V is a constant of 1 or more.

  The calculation unit 35 can refer to the setting of the retransmission flag in the communication packet table 23 when determining the value of V. When the retransmission flag is set to “ON”, the calculation unit 35 makes the value of V smaller than when the retransmission flag is set to “OFF”. For example, since the connection is established before it is determined whether the transmission source device 2 is the target device, the retransmission flag is set to “OFF”. Therefore, in order to determine whether the transmission source device 2 autonomously performs retransmission at a time corresponding to the response time, the calculation unit 35 sets the value of V to a value larger than 1 and calculates the standby time. For example, the calculation unit 35 can calculate the waiting time when resending a packet transmitted from the transmission source device 2 that is not determined to be the target device as V = 3. On the other hand, for the connection for which the retransmission flag is set to “ON”, since the communication device 10 has decided to retransmit the packet transmitted from the transmission source device 2 to the opposite device 6, the calculation unit 35 The waiting time can be calculated by setting the value of V to 1.

[Resend packet]
The communication device 10 confirms whether the packet transmitted from the transmission source device 2 is received by the opposite device 6 by referring to the confirmation response number in the response message. The confirmation response number is a sequence number indicating the head of data received by the opposite apparatus 6 next to the data included in the packet corresponding to the response message. For example, when receiving the packet P1, since the opposite device 6 has received 1000 bytes from the data of sequence number = 2001, the confirmation response number is 3001 in the response message A1 to the packet P1.

  The response message A1 received by the communication device 10 is output to the measurement unit 34 via the reception unit 11 and the directly connected device detection unit 31. When the measurement unit 34 confirms that the value of the ACK bit in the TCP header of the response message A1 is “1”, the measurement unit 34 acquires the confirmation response number. The measurement unit 34 determines that the packet associated with the sequence number smaller than the confirmation response number included in the response message has been received by the opposite device 6, and data corresponding to the sequence number smaller than the confirmation response number. Or delete the packet. Further, the measurement unit 34 deletes the packet corresponding to the received response message and the data related to the packet corresponding to the response message from the communication packet table 23. FIG. 9 shows the communication packet table 23 after information related to the packet P1 is deleted based on the response message A1.

  On the other hand, if the notification that the packet is received by the opposite device 6 does not arrive within the waiting time, the packet is retransmitted. The retransmission of the packet from the communication device 10 to the opposite device 6 includes a case where a packet stored in the communication device 10 is retransmitted to the opposite device 6 and a case where the transmission source device 2 retransmits the packet. The operation of the communication device 10 will be described for each case.

(A) Case 1
First, a case where a packet stored in the communication device 10 is retransmitted to the opposite device 6 will be described. The determination unit 36 determines whether to perform transmission from the communication device 10 for each connection for which the retransmission flag is set to OFF. The determination unit 36 acquires the current time from the timer 14 and obtains a difference from the transmission time included in the communication packet table 23. When the obtained difference exceeds the standby time obtained by the calculation unit 35, the determination unit 36 determines to retransmit the packet from the communication device 10. The determination unit 36 notifies the retransmission unit 37 of a packet to be retransmitted. Further, the determination unit 36 sets the retransmission flag of the connection table 22 to ON for the connection used for transmission of the packet determined to be retransmitted.

  For example, in the connection used for transmitting a packet from the port 1300 of the transmission source device 2 (IP1) to the port 1400 of the opposite device 6 (IP10), the RTO calculation value is 0.12 seconds. To do. Further, it is assumed that the first waiting time calculated by the calculation unit 35 is 0.12 × (2 ^ 0) × 3 = 0.36 (seconds). Assume that the determination unit 36 refers to the communication packet table 23 of FIG. 9 at 12: 00: 0.612 seconds. In this case, the difference between the current time and the transmission time is 12: 00: 0.612 seconds-12: 0: 0.212 seconds = 0.400 seconds. Therefore, the determination unit 36 determines to retransmit the packet P <b> 2 by the communication device 10 and notifies the retransmission unit 37. Further, the determination unit 36 sets the retransmission flag in the connection table 22 to ON. That is, the connection table 22 is changed from FIG. 8B to FIG. 10A.

  The retransmission unit 37 changes the number of retransmissions in the communication packet table 23 to 1 for the packet notified from the determination unit 36 and instructs the transmission unit 12 to perform retransmission. Further, the retransmission unit 37 updates the transmission time of the communication packet table 23 to the time when the packet is retransmitted. An example of the communication packet table 23 after the change is shown in FIG. Even after the transmission unit 12 is instructed to retransmit the packet, the retransmission unit 37 periodically elapses from the transmission time for the packet transmitted to the opposite device 6 through the connection in which the retransmission flag is set to ON. Ask for time. The retransmission unit 37 instructs the transmission unit 12 to perform a second retransmission for a packet whose time elapsed from the transmission time exceeds the second standby time. Thereafter, whenever the difference between the transmission time and the time at which the retransmission unit 37 confirms the communication packet table 23 exceeds the standby time, the retransmission unit 37 instructs the transmission unit 12 to retransmit the packet.

  Next, retransmission of a packet transmitted to the opposite apparatus 6 via a connection in which the retransmission flag is set to ON will be described. For retransmission of a packet transmitted via a connection for which the retransmission flag is set to ON, the calculation unit 35 can calculate the standby time with V = 1. The calculation unit 35 stores the obtained standby time in the storage unit 20 as appropriate. In this case, the retransmission unit 37 instructs the transmission unit 12 to retransmit a packet recorded in the communication packet table 23 even if the standby time obtained as V = 1 in equation (2) from the transmission time is exceeded. For example, for the packet P3, the retransmission unit 37 instructs retransmission to the opposite device 6 at the time when the standby time calculated with V = 1 for the connection has elapsed. Further, the retransmission unit 37 updates the transmission time of the communication packet table 23 to the time when the packet is retransmitted.

  In this example, an example has been described in which the communication apparatus 10 performs retransmission for a connection in which retransmission is not performed even after a time three times longer than the retransmission timeout has elapsed, but the communication apparatus 10 is determined to perform retransmission. The criteria for doing so may be arbitrarily changed depending on the implementation. The calculation unit 35 calculates the standby time according to a criterion for retransmission at the communication device 10. Furthermore, when retransmission is not performed for a time longer than a predetermined threshold, such as 3 seconds, the determination unit 36 can also determine to perform retransmission by the communication device 10. In this case, the determination unit 36 determines that the communication device 10 performs retransmission for a connection that is not retransmitted even after the threshold time stored in advance has elapsed instead of the standby time calculated by the calculation unit 35. decide.

(B) Case 2
Next, the operation of the communication device 10 when the transmission source device 2 retransmits a packet will be described. First, the operation when the retransmission flag is not set will be described. The communication packet confirmation unit 33 compares the total value of the sequence number and data length of the input packet with NextSeqNo. If the total value is equal to or less than NextSeqNo, the communication packet confirmation unit 33 determines that the packet retransmitted from the transmission source device 2 has been acquired. Then, the communication packet confirmation unit 33 extracts an entry having the same connection and sequence number as the acquired packet from the communication packet table 23, and increments the value of the number of retransmissions of the extracted entry by one.

  Next, the communication packet confirmation unit 33 transmits the retransmitted packet from the transmission source device 2 to the opposite device 6 and notifies the determination unit 36 of information specifying the packet to be retransmitted. The determination unit 36 acquires the time when the notification is received from the communication packet confirmation unit 33 from the timer 14. Further, the determination unit 36 obtains the previous transmission time of the packet to be retransmitted from the communication packet table 23 and obtains the difference (actual timeout time) from the time obtained from the timer 14. The determination unit 36 compares the actual timeout time with the standby time. The calculation method of the waiting time is the same as in case 1. When the actual timeout time is longer than the waiting time, the determination unit 36 determines to retransmit the packet from the communication device 10 for the connection, and sets the retransmission flag of the connection table 22 to ON.

  After the determination unit 36 obtains the actual timeout time, the communication packet confirmation unit 33 instructs the transmission unit 12 to transmit a packet to be retransmitted, and updates the transmission time in the communication packet table 23 for the packet instructed to be transmitted. .

  For example, after the communication packet table 23 in FIG. 9 is generated, the transmission source device 2 transmits the packet P2 to the opposite device 6 before the communication device 10 retransmits the packet P2. Here, it is assumed that the standby time is calculated from the equation (2) with V = 2 for the connection in which the retransmission flag is set to OFF. It is assumed that the time when the communication device 10 transfers the packet P2 retransmitted from the transmission source device 2 to the opposite device 6 is 12: 00: 0.5. Then, the communication packet confirmation unit 33 increments the number of retransmissions once for the entry of the packet P2 shown in FIG. Since the transmission time of the packet P2 is 12: 00: 0.212 seconds, the determination unit 36 determines the actual timeout period from 12: 0: 0.5-12-12: 0: 0.212 seconds = 0.288 seconds. Is 0.288 seconds. Next, the determination unit 36 compares the standby time calculated for the connection with the actual timeout time. Here, if the RTO calculation value is 0.12 seconds, the waiting time is V = 2, so 0.12 × (2 × 0) × 2 = 0.24 (seconds). Therefore, the actual timeout time is longer than the waiting time. Therefore, the determination unit 36 determines to retransmit the packet from the communication device 10 for the connection used for transmission of the packet P2, and sets the retransmission flag of the connection to ON. Thereafter, the communication packet confirmation unit 33 instructs the transmission unit 12 to retransmit the packet P2 toward the opposite device 6. For packet P2, the transmission time is changed to 12: 00: 0.5.

  In this example, the example in which the communication apparatus 10 performs retransmission when the actual timeout is twice or more the RTO calculation value has been described. However, the actual timeout and RTO for determining that the communication apparatus 10 performs retransmission are described. The ratio of calculated values may be changed arbitrarily depending on the implementation. Further, when the actual timeout time is longer than a predetermined time, such as 3 seconds, the determination unit 36 can also determine that the communication device 10 performs retransmission.

  Next, the packet transmitted to the opposite device 6 via the connection in which the retransmission flag is set to ON is processed in the same manner as in case 1. Therefore, for a connection in which the retransmission flag is already set to ON, for example, a packet stored in the communication device 10 when the standby time determined as V = 1 in Expression (2) from the transmission time has elapsed. Is retransmitted to the opposite device 6.

[Update of RTO calculation value]
Next, updating of the RTO calculation value will be described. Here, a case where the packet P1 is received by the opposite device 6 and a response message A1 regarding the packet P1 is transmitted from the opposite device 6 to the transmission source device 2 will be described as an example.

  The response message A1 received by the communication device 10 is output to the measurement unit 34 via the reception unit 11 and the directly connected device detection unit 31 as described above. The measuring unit 34 calculates a sequence number having a value smaller than the confirmation response number by the data length, and identifies the packet notified of reception by the response message. For example, in the response message A1, since the confirmation response number is 3001 and the data length is 1000 bytes, the measurement unit 34 recognizes that the response message for the packet having the sequence number of 3001-1000 = 2001 has been received. Then, the measurement unit 34 refers to the communication packet table 23 to obtain the time (transmission time) at which the packet that received the response message was transmitted from the transmission unit 12 to the opposite device 6. The measurement unit 34 sets a value obtained by subtracting the time from the reception time of the response message to the transmission time of the packet notified of reception as the response time.

For example, as illustrated in FIG. 8A, the time when the packet P1 is transmitted from the communication device 10 to the opposite device 6 is 12 hours 0 minutes 0.21 seconds. The measurement unit 34 acquires the reception time of the response message A1 from the timer 14. For example, it is assumed that the reception time of the response message A1 is 12: 00: 0.41 seconds. Then, the measurement unit 34
(12: 00: 0.41 seconds) − (12: 0: 0.21 seconds) = 0.20 seconds is the response time. The measurement unit 34 outputs the obtained response time to the calculation unit 35. When the calculation unit 35 updates the RTO calculation value, the calculation unit 35 obtains the update value by the expression (3). In the equation (3), the N-th calculated RTO value is RTO _{cal , N.}
RTO _{cal , N} = SRTT _N + max (G, K × RTTVAR _N ) (3)
here,
K = 4
RTTVAR _N = (1−β) × RTTVAR _N−1 + β × | SRTT _N−1 −MRTT _N |
SRTT _N = (1−α) × SRTT _N−1 + α × MRTT _N
Suppose that Here, it is assumed that α = 1/8 and β = 1/4. N is an arbitrary integer of 2 or more. MRTT _N is a response time obtained by the measurement unit 34 for the Nth time. G is the granularity (resolution) of the clock used by the communication device 10 for measuring the response time. The method for obtaining the standby time based on the updated RTO calculation value is as described above. When the standby time is calculated by the calculation unit 35, retransmission processing is performed based on the standby time.

[Process when communication ends]
When the RST or FIN in the TCP header is 1, the connection detection unit 32 deletes information corresponding to the connection from which the packet has been transmitted from the connection table 22. Accordingly, established connections are recorded in the connection table 22, and no lost connections or connections that are requested to be disconnected from the transmission source device 2 are recorded. In addition, the packet transmitted via the connection to be deleted and information related to the packet are also deleted from the communication packet table 23. Furthermore, as described above, each time the directly connected device detection unit 31 receives a packet, it updates the last communication time associated with the source address of the received packet. Therefore, the directly connected device detection unit 31 deletes the entry in which the difference between the last communication time and the current time is a certain time or more from the directly connected device table 21.

  11A and 11B are flowcharts for explaining an example of an operation performed when the communication device 10 receives a packet. Hereinafter, the operation of the communication apparatus 10 will be described with reference to FIGS. 11A and 11B. Note that the operation of the communication device 10 illustrated in FIGS. 11A and 11B is an example, and may be changed depending on the implementation. For example, steps S3 and S4 can be switched in order. In step S5, the combination and order of steps S14 and S15 may be changed. Further, any combination of the operations of steps S17 and S18, the combinations of steps S19 and S20, and the combinations of steps S1 and S2 may be performed first.

  The directly connected device detection unit 31 confirms whether there is a directly connected device that has not been communicated via the communication device 10 for a certain time or longer, and deletes the registration of the directly connected device that has not been communicated from the directly connected device table 21. (Steps S1, S2). When the reception unit 11 receives the packet, the directly connected device detection unit 31 confirms whether the received packet is an ARP packet (step S3). If the received packet is not an ARP packet, the directly connected device detection unit 31 confirms whether the received packet is a TCP packet (step S4). When the received packet is a TCP packet, the direct connection device detection unit 31 compares the transmission source address with the address recorded in the direct connection device table 21 to confirm whether the transmission source device is a direct connection device ( Step S5). When the transmission source device is a direct connection device, the connection detection unit 32 confirms whether or not the connection set from the transmission source device 2 to the opposite device 6 is registered in the connection table 22 (Yes in step S5). Step S6). When the connection is not registered in the connection table 22, the connection detection unit 32 registers a connection for transmitting data from the transmission source device 2 to the opposite device 6 in the connection table 22 (No in step S6, step S7). .

  Next, the communication packet confirmation unit 33 confirms whether the received packet is a retransmitted packet by comparing the total value of the sequence number of the received packet and the data length with NextSeqNo in the connection table 22 (step S8). ). If the total value of the sequence number and data length of the received packet is equal to or less than NextSeqNo, the communication packet confirmation unit 33 determines that the packet is a retransmission and updates the communication packet table 23 (Yes in step S8, step S9). On the other hand, when the total value of the sequence number and the data length of the received packet is larger than NextSeqNo, the communication packet confirmation unit 33 determines that the processing target packet is not a retransmitted packet. The communication packet table 23 updates NextSeqNo of the connection table 22 to the total value of the sequence number and data length of the received packet, and further updates the communication packet table 23 (No in step S8, step S10).

  When the retransmitted packet is received, the determination unit 36 obtains a time (actual timeout time) between the time when the retransmitted packet is transmitted and the time when the same packet is first transmitted to the opposite device 6. Furthermore, the determination unit 36 determines whether the actual timeout time exceeds the standby time (step S11). When the actual timeout time exceeds the standby time, the determination unit 36 determines to retransmit the packet to the opposite device 6 in accordance with the standby time calculated by the calculation unit 35, and sets the retransmission flag to ON. Set (Yes in step S11, step S12).

  Next, the communication device 10 confirms whether the received packet is a response message. This process is also performed when the source address of the received packet is not registered in the directly connected device table 21 (No in step S5, step S13). The directly connected device detection unit 31 confirms whether the destination address of the received packet is recorded in the directly connected device table 21. Further, the measurement unit 34 confirms whether the value of the ACK bit in the TCP header of the received packet is 1 (step S13). If the destination address is recorded in the directly connected device table 21 and ACK is 1, the measurement unit 34 determines that the received packet is a response message. Further, the measurement unit 34 deletes the record about the packet notified by the counter device 6 by the response message from the communication packet table 23 (step S14). Thereafter, the last communication time in the connection table 22 is updated (step S15). On the other hand, when the received packet is not a response message, the last communication time in the connection table 22 is updated (No in step S13, step S15).

  Further, the connection detection unit 32 determines whether there is a connection that has not been communicated for a certain period of time among the connections included in the connection table 22 (step S16). If there is a connection that has not been communicated for a certain period of time, the connection detection unit 32 deletes the entry in the connection table 22 for that connection. Further, the communication packet confirmation unit 33 deletes the record of the packet transmitted through the connection that is not performing communication from the communication packet table 23 (step S17). Further, the connection detection unit 32 confirms whether there is a connection to be disconnected among the packets registered in the connection table 22 (step S18). This check is performed by checking whether the value of the RST bit or the FIN bit included in the TCP header of the received packet is 1. The connection detection unit 32 deletes the entry of the connection to be disconnected from the connection table 22. Further, the communication packet confirmation unit 33 deletes the record of the packet transmitted via the connection that is not performing communication from the communication packet table 23 (step S19).

  On the other hand, when the received packet is an ARP packet, the directly connected device detection unit 31 confirms whether the device that has transmitted the ARP packet is registered in the directly connected device table 21 (step S20). When the transmission source device of the ARP packet is not registered in the direct connection device table 21, the direct connection device detection unit 31 registers the IP address or the MAC address of the transmission source device in the direct connection device table 21 (step S21). When the received packet is an ARP packet, the process after step S15 is performed after the process of step S21. If the transmission source address has already been registered in the directly connected device table 21, the processing after step S15 is performed after the processing at step S20. Further, even when the type of the received packet is not a TCP packet, the processing after step S15 is performed (No in step S4, step S15).

  FIG. 12 is a flowchart for explaining an example of the operation when a packet stored in the communication device 10 is retransmitted to the opposite device 6. FIG. 12 shows an example of the operation. For example, there is a case where a change is made such that the order is changed so that steps S34 and S35 are performed before step S31. FIG. 12 shows the operation when the determination unit 36 is periodically started. For example, the determination unit 36 seems to be continuously activated while the communication device 10 is activated. It may be deformed. Furthermore, the interval at which the determination unit 36 is activated is set to an arbitrary value.

  The determination unit 36 obtains the difference between the transmission time and the current time included in the communication packet table 23, and confirms whether there is a packet for which the obtained difference exceeds the standby time (step S31). Here, the standby time is calculated from the equation (2) based on the RTO calculation value. If there is a packet that has not been retransmitted even after the waiting time has been exceeded, the retransmission unit 37 instructs the transmission unit 12 to retransmit the packet. Further, the retransmission unit 37 updates the transmission time of the communication packet table 23 for the packet instructed to be retransmitted (Yes in step S31, step S32). Further, the determination unit 36 sets the retransmission flag to ON for the connection used for transmission of the retransmitted packet (step S33).

  Next, the retransmission unit 37 does not retransmit a packet transmitted via a connection in which the retransmission flag is set to ON even if the standby time calculated as V = 1 from the transmission time is exceeded. It is confirmed whether the packet is recorded in the communication packet table 23 (step S34). When the corresponding packet is recorded in the communication packet table 23, the retransmission unit 37 instructs the transmission unit 12 to retransmit the packet. Further, the retransmission unit 37 updates the transmission time of the communication packet table 23 for the packet instructed to be retransmitted (Yes in step S34, step S35).

  FIG. 13 is a table showing an example of the time from when a packet transmitted to the opposite apparatus 6 is transmitted until it is retransmitted. In this example, in the transmission source device 2, it is assumed that the retransmission timeout is fixed to 3 seconds. That is, the transmission source device 2 does not retransmit a packet unless 3 seconds or more have elapsed after the transmission of the packet.

  If retransmission from the communication apparatus 10 is not performed, retransmission from the transmission source apparatus 2 is performed for the first time after 3 seconds from transmission, as shown in FIG. If no response message is obtained even after the first retransmission, the transmission source device 2 sets the waiting time until the next retransmission to twice the length of the first retransmission, The second retransmission is performed 9 seconds after the transmission.

  On the other hand, the waiting time when retransmission is performed based on the determination of the determination unit 36 for the packet with the retransmission flag OFF is shown in (B). Here, it is assumed that the RTO calculation value calculated from the response time of the connection is 0.12 seconds. In addition, when the determination unit 36 cannot confirm reception by the opposite device 6 within a time within three times the RTO calculation value and the packet is not retransmitted, the communication device 10 retransmits the packet. Shall be determined. In this case, the first retransmission is performed 0.36 seconds after the first packet transmission. Also, a second retransmission is performed 1.08 seconds after the packet is first transmitted, a third retransmission is performed 2.52 seconds later, and a fourth retransmission is performed 5.4 seconds later.

  Therefore, when transmission is performed in accordance with the standby time obtained based on the RTO calculation value calculated from the response time, as shown in (B), the packet is retransmitted four times within 10 seconds from the first transmission. Is done. On the other hand, when the communication apparatus 10 does not perform retransmission, as shown in (A), retransmission is performed only twice within 10 seconds after the first packet transmission.

  Further, for a connection for which the retransmission flag is set to ON, the communication apparatus 10 does not perform the retransmission process of the transmission source apparatus 2 unless three or more times the RTO calculation value has elapsed since the packet was first transmitted. Recognize. Accordingly, the calculation unit 35 can set the value of V in equation (2) or the like to 1 when calculating the standby time, and retransmission is performed at the timing shown in (C). Then, retransmission is performed six times within 10 seconds after the first packet transmission.

  In this way, in the system in which the communication device 10 calculates the standby time according to the response time and resends the packet when the standby time has elapsed since the packet was transmitted, even if a packet lost occurs, Retransmission is performed to the device 6. When data included in a packet transmitted from the transmission source device 2 is processed by an application operating in the opposite device 6, it is desirable that the packet can be retransmitted before a timeout occurs in the application. By retransmitting the packet stored in the communication device 10 from the communication device 10 to the opposite device 6, the packet retransmission timing can be set in accordance with the response time. Therefore, if the response time is short, even if the retransmission timeout at the transmission source device 2 is a fixed value, the number of retries until the application times out can be increased by the communication device 10 performing retransmission. . For example, when such a communication device 10 is arranged in a network to which a client device of a cloud computing system belongs, the number of retries can be increased even when the timing of retransmission performed by the transmission source device 2 is fixed. it can.

  Further, even when the retransmission timeout of the transmission source device 2 is not a fixed value, the number of retries may be increased by using the communication device 10. For example, when the transmission source device 2 retransmits a packet after waiting for a longer time than the standby time calculated by the communication device 10, the communication device 10 retransmits the packet on behalf of the transmission source device 2, so that the number of retries Will increase.

<Second Embodiment>
In the first embodiment, a case has been described in which the communication device 10 determines whether to retransmit a packet for each connection. However, in this embodiment, whether to perform retransmission in the communication device 10 is determined for each packet. . Therefore, whether to retransmit in the communication device 10 is determined every time the packet transmitted from the transmission source device 2 to the opposite device 6 is retransmitted.

  14A and 14B are flowcharts illustrating an example of an operation performed when the communication apparatus 10 receives a packet. The processes of steps S41 to S50 are performed in the same manner as steps S1 to S10 described with reference to FIGS. 11A and 11B. Next, the determination unit 36 obtains an actual timeout time for the packet transmitted from the transmission source device 2 to the opposite device 6. The actual timeout time is the difference between the transmission time recorded in the retransmitted communication packet table 23 and the transmission time of the packet to be retransmitted. The determination unit 36 compares the actual timeout time with the standby time obtained using the RTO calculated value. (Step S51). When the actual timeout time is equal to or shorter than the standby time, the determination unit 36 sets the retransmission flag to “OFF” (step S52). On the other hand, when the actual timeout time is longer than the standby time, the determination unit 36 sets the retransmission flag to “ON” (step S53). The process of steps S54 to S62 is the same as that of steps S13 to S21.

In the present embodiment, whether or not to perform retransmission in the communication device 10 is determined every time the standby time elapses. For example, even if the retransmission flag is erroneously set to “ON”, the determination unit 36 The setting of the retransmission flag can be corrected when determining whether to retransmit the next packet. The present invention is not limited to the above-described embodiment, and can be variously modified. For example, the directly connected device detection unit 31 can also check whether the transmission source device is a directly connected device using the MAC address of the received packet. In this case, the directly connected device detection unit 31 confirms the Ethernet header of the received packet.

The following additional notes are further disclosed for each of the embodiments including the first and second embodiments described above.
(Appendix 1)
A receiving unit that receives the first and second packets from a transmission source device that transmits the first and second packets addressed to the opposite device and retransmits a packet that cannot be confirmed by the opposite device to the opposite device. When,
A storage unit for storing the first and second packets;
A transmitter for transmitting the first and second packets to the opposite device;
Time from the time when the transmission unit transmits the first packet to the opposite device to the time when the reception unit receives the first response message notifying the reception of the first packet at the opposite device A measurement unit for measuring the response time,
Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite device, the reception unit notifies the reception of the second packet by the opposite device. When not receiving a second response message and not receiving a retransmission packet that is a packet obtained by retransmitting the second packet from the transmission source device, the second packet is acquired from the storage unit, and A communication apparatus comprising: a retransmission unit that causes the transmission unit to transmit the second packet to the opposite device again.
(Appendix 2)
Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite apparatus, the reception unit receives neither the second response message nor the retransmission packet. A packet addressed to the opposite device received from the transmission source device after the second packet is determined to be a target to be retransmitted by the retransmission unit, and a determination unit that designates the transmission source device as a target device; ,
The retransmission unit from the time when the third packet transmitted after the second packet from the target device is transmitted from the transmission unit to the time when the transmission unit is instructed to retransmit the third packet. A calculation unit for calculating a waiting time that is a waiting time;
If the response message for the third packet is not received even after the waiting time has elapsed from the time when the third packet was transmitted from the transmission unit, the retransmission unit receives the third packet as the opposite device. The communication apparatus according to appendix 1, wherein:
(Appendix 3)
The time from when the third packet is transmitted from the transmission unit to the opposite device until the reception unit receives the third packet retransmitted from the transmission source device is the waiting time. The communication device according to appendix 2, wherein the determination unit determines that the transmission source device is no longer the target device.
(Appendix 4)
The establishment of a connection used for data transmission from the transmission source device to the opposite device is detected, and data transmitted via the connection is next to data included in a packet transmitted via the connection. A connection detection unit that records a first value to be identified in the connection table in association with the connection;
The retransmission unit specifies data transmitted via the connection next to data included in the packet received by the reception unit as a packet addressed to the opposite device transmitted via the connection. When the value of 2 is less than or equal to the value recorded in the connection table, it is recognized that the packet including the data specified by the second value is retransmitted from the transmission source device. The communication apparatus as described in.
(Appendix 5)
The connection detection unit confirms the end of communication via the first connection by checking a control bit included in a packet transmitted / received via the first connection recorded in the connection table. If detected, the entry related to the first connection is deleted from the connection table.
(Appendix 6)
The communication device according to any one of appendices 1 to 5, wherein when the reception unit receives a response message, the storage unit deletes a packet corresponding to the received response message.
(Appendix 7)
Receiving the first and second packets from a transmission source device that transmits first and second packets addressed to the opposite device, and retransmits a packet that cannot be confirmed by the opposite device to the opposite device;
Storing the first and second packets;
Sending the first and second packets to the opposite device;
Measure response time, which is the time between the time when the first packet is transmitted to the opposite device and the time when the first response message for notifying the reception of the first packet at the opposite device is received. And
Even if a time longer than the response time has elapsed since the time when the second packet was transmitted to the opposite device, a second response message for notifying the reception of the second packet by the opposite device should be received. In addition, when the retransmission packet which is a packet obtained by retransmitting the second packet is not received from the transmission source device, a process of transmitting the second packet to the opposite device again is transmitted from the transmission source device. And a communication apparatus that relays the packet addressed to the opposite apparatus.
(Appendix 8)
Receiving the first and second packets from a transmission source device that transmits first and second packets addressed to the opposite device, and retransmits a packet that cannot be confirmed by the opposite device to the opposite device;
Storing the first and second packets;
Sending the first and second packets to the opposite device;
Measure response time, which is the time between the time when the first packet is transmitted to the opposite device and the time when the first response message for notifying the reception of the first packet at the opposite device is received. And
Even if a time longer than the response time has elapsed since the time when the second packet was transmitted to the opposite device, a second response message for notifying the reception of the second packet by the opposite device should be received. And, when a retransmission packet that is a packet obtained by retransmitting the second packet is not received from the transmission source device, the computer is caused to execute a process of retransmitting the second packet to the opposite device. Communication program.

2 Source device 4 WAN
6 Opposing Device 10 Communication Device 11 Receiving Unit 12 Transmitting Unit 13 Routing Unit 14 Timer 20 Storage Unit 21 Directly Connected Device Table 22 Connection Table 23 Communication Packet Table 24 Routing Table 30 Retransmission Alternative Unit 31 Directly Connected Device Detection Unit 32 Connection Detection Unit 33 Communication Packet Confirmation unit 34 Measurement unit 35 Calculation unit 36 Determination unit 37 Retransmission unit

Claims (7)

A receiving unit that receives the first and second packets from a transmission source device that transmits the first and second packets addressed to the opposite device and retransmits a packet that cannot be confirmed by the opposite device to the opposite device. When,
A storage unit for storing the first and second packets;
A transmitter for transmitting the first and second packets to the opposite device;
Time from the time when the transmission unit transmits the first packet to the opposite device to the time when the reception unit receives the first response message notifying the reception of the first packet at the opposite device A measurement unit for measuring the response time,
Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite device, the reception unit notifies the reception of the second packet by the opposite device. When not receiving a second response message and not receiving a retransmission packet that is a packet obtained by retransmitting the second packet from the transmission source device, the second packet is acquired from the storage unit, and A retransmission unit that causes the transmission unit to transmit the second packet to the opposite device again ;
When the retransmission packet is received from the transmission source device, an actual time-out time that is a difference between the reception time of the retransmission packet and the time of transmission of the second packet is determined from the transmission of the second packet to the second packet. A determination unit that determines that a packet addressed to the opposite device received from the transmission source device after the second packet is a target of a retransmission process when the retransmission time is longer than a standby time until a time instructing the transmission unit to transmit A communication apparatus comprising: A receiving unit that receives the first and second packets from a transmission source device that transmits the first and second packets addressed to the opposite device and retransmits a packet that cannot be confirmed by the opposite device to the opposite device. When,
A storage unit for storing the first and second packets;
A transmitter for transmitting the first and second packets to the opposite device;
Time from the time when the transmission unit transmits the first packet to the opposite device to the time when the reception unit receives the first response message notifying the reception of the first packet at the opposite device A measurement unit for measuring the response time,
Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite device, the reception unit notifies the reception of the second packet by the opposite device. When not receiving a second response message and not receiving a retransmission packet that is a packet obtained by retransmitting the second packet from the transmission source device, the second packet is acquired from the storage unit, and A retransmission unit that causes the transmission unit to transmit the second packet to the opposite device again;
Even if a time longer than the response time elapses from the time when the transmission unit transmits the second packet to the opposite apparatus, the reception unit receives neither the second response message nor the retransmission packet. A determination unit that determines that a packet addressed to the opposite device received from the transmission source device after the second packet is a target of retransmission processing, and designates the transmission source device as a target device;
The retransmission unit from the time when the third packet transmitted after the second packet from the target device is transmitted from the transmission unit to the time when the transmission unit is instructed to retransmit the third packet. for example Bei the calculation unit for calculating the waiting time is the time to wait,
A response message to said third packet, when the third packet is not received even after the standby time from the time transmitted from the transmitting unit, the retransmission unit in the transmitting unit, the third packet you characterized in that Ru is transmitted to the counter device communication device. The time from when the third packet is transmitted from the transmission unit to the opposite device until the reception unit receives the third packet retransmitted from the transmission source device is the waiting time. The communication device according to claim 2, wherein the determination unit determines that the transmission source device is no longer the target device. The establishment of a connection used for data transmission from the transmission source device to the opposite device is detected, and data transmitted via the connection is next to data included in a packet transmitted via the connection. A connection detection unit that records a first value to be identified in the connection table in association with the connection;
The retransmission unit specifies data transmitted via the connection next to data included in the packet received by the reception unit as a packet addressed to the opposite device transmitted via the connection. 3. When the value of 2 is less than or equal to the value recorded in the connection table, it is recognized that a packet including data specified by the second value is retransmitted from the transmission source device. 3. The communication device according to 3. The connection detection unit confirms the end of communication via the first connection by checking a control bit included in a packet transmitted / received via the first connection recorded in the connection table. The communication apparatus according to claim 4, wherein when detected, an entry related to the first connection is deleted from the connection table. Receiving the first and second packets from a transmission source device that transmits first and second packets addressed to the opposite device, and retransmits a packet that cannot be confirmed by the opposite device to the opposite device;
Storing the first and second packets;
Sending the first and second packets to the opposite device;
Measure response time, which is the time between the time when the first packet is transmitted to the opposite device and the time when the first response message for notifying the reception of the first packet at the opposite device is received. And
Even if a time longer than the response time has elapsed since the time when the second packet was transmitted to the opposite device, a second response message for notifying the reception of the second packet by the opposite device should be received. not, and, when said from the source device does not even receive the retransmission packet is the second packet retransmission packet, sends again the second packet to the opposite apparatus,
When the retransmission packet is received from the transmission source device, an actual time-out time that is a difference between the reception time of the retransmission packet and the time of transmission of the second packet is determined from the transmission of the second packet to the second packet. If the transmission time is longer than the waiting time until the time to retransmit the packet, a process for determining that a packet addressed to the opposite device received from the transmission source device after the second packet is a target of retransmission processing is performed from the transmission source device. A communication method executed by a communication device that relays a packet addressed to the opposite device. Receiving the first and second packets from a transmission source device that transmits first and second packets addressed to the opposite device, and retransmits a packet that cannot be confirmed by the opposite device to the opposite device;
Storing the first and second packets;
Sending the first and second packets to the opposite device;
Measure response time, which is the time between the time when the first packet is transmitted to the opposite device and the time when the first response message for notifying the reception of the first packet at the opposite device is received. And
Even if a time longer than the response time has elapsed since the time when the second packet was transmitted to the opposite device, a second response message for notifying the reception of the second packet by the opposite device should be received. not, and, when said from the source device does not even receive the retransmission packet is the second packet retransmission packet, sends again the second packet to the opposite apparatus,
When the retransmission packet is received from the transmission source device, an actual time-out time that is a difference between the reception time of the retransmission packet and the time of transmission of the second packet is determined from the transmission of the second packet to the second packet. If it is longer than the waiting time until the time to retransmit the packet , the computer is caused to execute processing for determining that a packet addressed to the opposite device received from the transmission source device after the second packet is a target of retransmission processing. A featured communication program.

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